The search for the development of tunable organic fluorophores with improved properties are of great interest. Fluorophores with attractive and efficient emission characteristics are desirable for applications in biological science, material science application such as organic light emitting diodes (OLEDs) and sensing applications. Reference may be made to: a) E. M. Nolan, S. J. Lippard, Chem. Rev. 2008, 108, 3443; b) Applied Fluorescence in Chemistry, Biology, and Medicine (Eds.: W. Rettig, B. Strehmel, S. Schrader, H. Seifert), Springer, New York, 1999; c) A. C. Grimsdale, K. L. Chan, R. E. Martin, P. G. Jokisz, A. B. Holmes, Chem. Rev. 2009, 109, 897; d) S. M. Kelly in Flat Panel Displays: Advanced Organic Materials (Ed.: J. A. Connor), The Royal Society of Chemistry, Cambridge, 2000; e) S. Park, J. E. Kwon, S. H. Kim, J. Seo, K. Chung, S.-Y. Park, D.-J. Jang, B. M. Medina, J. Gierschner, S. Y. Park, J. Am. Chem. Soc. 2009, 131, 14043; f) Y. Yamaguchi, Y. Matsubara, T. Ochi, T. Wakamiya, Z.-I. Yoshida, J. Am. Chem. Soc. 2008, 130, 113867; g) Z. M. Hudson, S. Wang, Acc. Che. Res. 2009, 42, 1584; g) H. S. Joshi, R. Jamshidi, Y. Tor, Angew. Chem. Int. Ed. 1999, 38, 2722;
A critical element in designing and fabricating such materials is the control of their emission wavelength. Blue-, green- and red-light-emitting materials are needed for full-color displays. For organic molecules this is often achieved by chemically modifying the π-conjugation or the substituent group; which include substitution with stronger donor or acceptor moieties. This will effectively modulate the HOMO-LUMO gap of the molecules. An alternative approach for controlling the emitted color of organic materials is to append fluorescent chromophores to a polymeric backbone or to blend such dyes into inert polymeric matrices. Reference may be made to: a) Y. Yamaguchi, T. Tanaka, S. Kobayashi, T. Wakamiya, Y. Matsubara, Z.-I. Yoshida, J. Am. Chem. Soc. 2005, 127, 9332; b) R. Abbel, C. Grenier, M. J. Pounderoijen, J. W. Stouwdam, P. E. L. G. Leclere, R. P. Sijbesma, E. W. Meijer, A. P. H. J. Schenning, J. Am. Chem. Soc. 2009, 131, 833; c) G. Kwak, H. Kim, I.-K. Kang, S.-H. Kim, Macromolecules, 2009, 42, 1733.
Light emitting devices can be used in displays (eg., flat-panel displays), screens such as computer screens and other items that require illumination. The brightness of the light emitting device is an important feature of the device. Solid state light emitting devices including LED's are extremely useful because of their low fabrication costs and long term durability. Reference may be made to: Rubner et al. U.S. Pat. No. 6,548,836, Baretz et al. U.S. Pat. No. 6,600,175. As the organic luminescent material, organic dyes emitting fluorescence such as 8-quinolinol aluminium complex or coumarin compounds are used. Although the organic light emitting diode has high luminescent characteristics, they involve a problem in the stability upon light emission or half life. Reference may be made to: Hirose et al. U.S. Pat. No. 6,670,052
An organic light-emitting device in which an oxazole-, thiazole- or imidazole-fused phenanthroline molecule is used as an emissive layer by Chen et al. U.S. Pat. No. 7,179,542, U.S. Pat. No. 6,713,781.
So far, a variety of strategies have been worked out to realize high solid state emission. The modulation of optical-band gap by changing the strength of donor-acceptor have been shown by Ajayaghosh and coworkers. Reference can be made to: a) A. Ajayaghosh, V. K. Praveen, S. Srinivasan, and R. Varghese, Adv. Mater. 2007, 19, 411; b) C. Vijayakumar, V. K. Praveen, and A. Ajayaghosh Adv. Mater. 2009, 21, 2059, Ajayaghosh et al. PCT/IN2008/000372. Recently the emission of the three primary colors (blue, green and red) simultaneously with equal intensities to produce white light and the pure colors separately in a tunable way was achieved from a single component emitter. Reference can be made to: G. He, D. Guo, C. He, X. Zhang, X. Zhao, and C. Duan; Angew. Chem. Int. Ed. 2009, 48, 6132.
But the rational design of fluorescent probes with appreciable quantum yield in solid state is still a challenging task. Therefore the demand for the design and development of efficient fluorescent materials are always a matter of scientific concern. In the present invention we put forward a simple and easy protocol for developing organic luminescent materials with high solid-state emission useful for fabricating multicolor light emitting devices. The conversion of UV light into visible light is also demonstrated by coating the color tunable materials on the 365-nm emitting solid state LED.
Another application f fluorophores is for sensing of cations, anions and neutral molecules. Reference can be made to: a) A. P. de Silva, H. Q. Gunaratne, T. Gunnlaugsson, A. J. M. Huxely, C. P. McCoy, J. T. Rademacher, T. E. Rice, Chem. Rev. 1997, 97, 1515; b) M. Takeuchi, M. Ikeda, A. Sugasaki, S. Shinkai, Acc. Chem. Res. 2001, 34, 865; c) A. Ajayaghosh, Acc. Chem. Res. 2005, 38, 449; d) E. L. Que, D. W. Domaille, C. J. Chang, Chem. Rev. 2008, 108, 1517; e) E. Nolan, S. J. Lippard, Chem. Rev. 2008, 108, 3443; f) R. McRae, P. Bagchi, S. Sumalekshmy, C. J. Fahrni, Chem. Rev. 2009, 109, 4780; g) E. J. O'Neil, B. D. Smith, Chem. Soc. Rev. 2006, 250, 3068; h) S. W. Thomas III, G. D. Joly, T. M. Swager, Chem. Rev. 2007, 107, 1339.
Many of these sensors are specific either for a particular cation or anion. However, screening of a specific metal salts in terms of the associated counter anions remains challenging. For example, colorimetric and/or fluorimetric probes that sense a specific cation will not in general be able to differentiate the associated counteranions and vice-versa. Fluorophores with strong intramolecular charge transfer (ICT) shows substantial changes in fluorescence with respect to the surrounding environment (solvatochromic probes). One of the methods to impart solvatochromic property to a fluorophore is by functionalization with electron donor (D) and electron acceptor (A) moieties. Such a structure will cause significant variation in the dipole moment of the molecule between the ground state and excited state. If the donor and the acceptor moieties are weak, charge transfer occurs in the excited state thereby perturbing the fluorescence. Fluorophores with positive solvatochromism show red-shift in the emission maximum with low quantum yields on increasing the solvent polarity. In addition, solvatochromic probes will also be associated with change in fluorescence lifetime with respect to solvent polarity. Therefore, solvatochromic probes have been widely used for a variety of applications such as polarity sensitive live cell imaging, cation sensing, and for biosensing. However, solvatochromic fluorescence property has not been exploited for differentiating and identifying the counter anions involved in different salts of a specific cation. In the present invention we show that the fluorescent molecular probe of formula 2 is able to distinguish zinc salts with various counterions. Reference may be made to: a) Sunahara, H.; Urano, Y.; Kojima, H.; Nagano, T J. Am. Chem. Soc. 2007, 129, 5597; b) S. Maruyama, K. Kikuchi, T. Hirano, Y. Urano, T. Nagano, J. Am. Chem. Soc. 2002, 124, 10650; c) S. Sumalekshmy, M. M. Henary, N. Siegel, P. V. Lawson, Y. Wu, K. Schmidt, J.-L. Bredas, J. W. Perry, C. J. Fahrni, J. Am. Chem. Soc. 2007, 129, 11888.
Certain fluorescence probes are highly fluorescing when excited with one photon at a wavelength in UV or visible range. However such wavelengths are inconvenient for cell imaging and tissue imaging because of their low penetration power and also due to the absorption of tissues and cells at this wavelength. Such wavelength also result in significant autofluorescence and phototoxicity. In order for the probe to be used as a two photon imaging probe for cells, it should be specific for a particular analyte, have cell viability, and it should have good two photon absorption cross section.
Many of the two photon absorbing compounds satisfy the formula D-π-D, A-π-A, D-A-D and A-D-A, wherein D is an electron donor group, A is an electron acceptor group and π comprises a bridge of π-conjugated bonds connecting the donor and acceptor. Molecules with these forms can be designed to operate in methods where in the compounds undergo simultaneous two photon absorption. Asymmetric dyes with large two photon absorption cross section are prepared by Reinhardt et al. Reference may be made to: U.S. Pat. No. 5,770,737.
Novel two photon probe with high fluorescence quantum yield, high two photon absorption cross section and high photostability are used in a method of multi photon imaging. In that, the fluorophores are functionalized with moieties having the properties of covalent attachment onto proteins, antibodies, DNA and RNA. The two photon dyes with high fluorescence intensity in the environment of cell membranes useful for distinguising hydrophilic and hydrophobic domains of the cell membranes are utilized for the real-time imaging of lipid rafts. Reference may be made to: Belfield et al. U.S. Pat. No. 7,253,287, Cho et al. U.S. Pat. No. 7,511,167. Dipyrromethaneboron difluoride dyes and their conjugates used in bioanalytical assays that are based on two-photon excitation. Reference can be made to: Meltola et al. U.S. Pat. No. 7,763,439.